Many computer printing apparatuses, such as inkjet printers, include a removable input tray for holding a stack of media sheets and a sheet feeding mechanism for separating and delivering individual media sheets from the media stack to a media path in the printing apparatus. Typically, the input tray is provided with at least one adjustable edge guide and a fixed, reference side wall. This type of tray requires the user to load a stack of sheets against the reference side wall, and use the adjustable edge guide to bias the stack of sheets against the reference side wall. Proper positioning of the media sheets in the input tray is a first step in correctly feeding the media through the printing apparatus. It is desirable for each sheet to be aligned as accurately as possible when the sheet initially enters the media path. If the top sheet of the stack is not properly aligned when it enters the media path, the printed image on the sheet will be skewed. To facilitate the alignment of the media sheets, the reference side wall is conventionally provided with one or more datum members (or edge stops), against which the stack of sheets is biased. These datum members are usually permanently fixed on the reference side wall, e.g. molded parts of the side wall. As such, the alignment of the media sheets depends on the alignment of the input tray relative to the printing axis. Due to variations in manufactured parts, the input tray with fixed datum members may not be properly oriented when all the printer's parts are assembled. As a consequence, additional alignment mechanisms and skew correction mechanisms are required to ensure proper alignment of the input tray relative to the printing axis. Furthermore, when the datum members are worn out due to wear and tear overtime, the entire tray has to be replaced. Such replacement is costly. Therefore, there exists a need for a removable media input tray with improved datum members.